This invention relates to a hand lever apparatus for manipulating through cable means various driven members such as a throttle valve of an internal combustion engine, and in particular to a hand lever apparatus which is adapted to be mounted in the vicinity of grip portion of a handle in a portable working machine such as a hedge trimmer or a bush cutter and which is suited for manipulating the opening and closing of the throttle valve by means of a throttle cable.
In a portable working machine such as a hedge trimmer or a bush cutter, a hand lever apparatus for adjusting the opening degree of a throttle valve of an internal combustion engine is attached to a portion of a U-shaped handle or a bar handle which is in the vicinity of grip portion of these handles for controlling the output of the internal combustion engine by hand.
This hand lever apparatus is usually provided with a throttle trigger (a throttle lever) that can be manipulated with fingers of an operator, so that the opening degree of the throttle valve can be adjusted by turning this throttle lever. The throttle valve is usually biased in the direction of minimum opening degree (idling opening degree) so that the throttle valve is retained at this idling opening degree in a free condition. However, when the throttle cable is pulled beyond a predetermined distance thus losing a predetermined looseness, the opening of the throttle valve is shifted from the idling opening degree to a high speed revolution side.
As for the construction of the handle lever apparatus for adjusting the opening degree of the throttle valve as explained above, there are known two types, i.e. an idling opening degree automatic reset type wherein the throttle lever can be automatically returned together with the throttle valve to the original position (idling opening degree) when the throttle lever is released from the state of revolution manipulation; and an opening degree-fixed type wherein the throttle lever can be kept immobilized at a desired revolution manipulation position even if fingers are released from the throttle lever (see Japanese Utility Model Publication S/57-19944).
According to the handle lever apparatus of idling opening degree automatic reset type, the engine can be automatically returned to the idling condition whenever the throttle lever is released from the operating fingers, so that if the portable working machine is of the type where the rotational driving force of the engine is transmitted via a centrifugal clutch to a working portion such as a cutting blade, the centrifugal clutch is turned into a cut-off condition thus preventing the rotational driving force from reaching the working portion. Therefore, if any accident happens to occur, the movement of the working portion can be immediately stopped by immediately rendering the throttle valve to return to the idling opening degree, which is an advantage in terms of enhancing the operational safety. However, there are problems in this handle lever apparatus of idling opening degree automatic reset type that the throttle lever is required to be held always with fingers so as to keep the throttle lever at a desired revolution position, thus making it cumbersome in operating the throttle lever at an intermediate opening degree, thus giving a fatigue to the operating fingers, and making it difficult to keep the magnitude of manipulation (revolution speed) constant.
When easiness of use is taken into account, it is generally desired that the revolution manipulation lever that will be manipulated with fingers such as a throttle lever should be constructed such that it takes only two positions, i.e. a released position and a set position (grasping position) without requiring to take an intermediate opening degree. In other words, it is considered preferable in view of manipulability that the adjustment of the throttle valve to an intermediate opening (a partial opening) and to a full opening (WOT) should be effected by setting the throttle lever to the same revolution manipulation position (the set position).
On the other hand, a hand lever apparatus of the aforementioned opening degree-fixing type is free from the aforementioned problems accompanied with the handle lever apparatus of idling opening degree automatic reset type, i.e. the throttle lever can be kept in an immobilized state at a desired revolution manipulation position even if fingers are released from the throttle lever, thus allowing the fingers to become free so as to easily perform the working. In spite of these advantages however, if any accident happens to occur, the throttle lever position-retaining function of the hand lever apparatus is required to be canceled by way of a separate manipulation, i.e. it is impossible to immediately stop the movement of the working member, thus rendering the hand lever apparatus of opening degree-fixing type inferior in terms of safety as compared with the hand lever apparatus of idling opening degree automatic reset type.
In any of the idling opening degree automatic reset type or the opening degree-fixing type, it is required to readjust the revolution manipulation position of the throttle valve if the throttle valve is to be returned to the previous opening degree in resuming the work after the throttle lever is once left free for temporarily suspending the work (this kind of manipulation is frequently experienced in the case of the bush cutter). However, this readjustment operation is troublesome so that there is still left room for improvement in terms of manipulability.
With a view to overcome the aforementioned problems or to solve the subject matter involved in the conventional hand lever apparatus, the present assignee has proposed as set forth in Japanese patent application H/7-108340 a hand lever apparatus, which is provided with a main lever and a sub-lever both being adapted to be rotationally manipulated. According to this hand lever apparatus, the cable connected to a driven member is adapted to be pulled by the sub-lever through a turning member such as a movable pulley, and the turning member is adapted to be shifted by the main lever.
According to this hand lever apparatus, the opening degree of the throttle valve constituting a driven member can be adjusted by way of the cable and at the same time easily retained at a desired opening degree. Additionally, this hand lever apparatus is advantageous in that it is possible to immediately put the throttle valve back to the minimum opening degree (the idling opening degree) whereby assuring a high safety, that it is possible to avoid fingers from being tired in short time, and that it is possible to dispense with the readjustment of opening degree of the throttle valve when the throttle valve is desired to be set to the previous opening degree which has been set in advance before the throttle valve is returned to the idling opening degree.
However, since the length of a cable to be pulled by the main lever corresponds with the rotational angle of the main lever of the hand lever apparatus, a relatively large rotational manipulation angle of the main lever is required for pulling a sufficient length of the cable, thus making the hand lever apparatus disadvantageous in this respect. In order to assure this large rotational manipulation angle of the main lever, a relatively large space for allowing the rotation of the main lever is required between the grip portion of the handle and the main lever, resulting in an enlargement in size and an increase in weight of the apparatus. In particular, when the main lever protrudes outward from the handle to a large extent, the main lever frequently becomes an obstacle at the time of use or even at the time of non-use, whereby deteriorating the workability and manipulability of the hand lever apparatus.